Apparatus for driving an electric watch

ABSTRACT

An apparatus for driving an electric watch having a balance wheel which is driven electro-magnetically, wherein driving current is alternately applied in opposite directions to the driving coil.

United States Paten [191 Fujita APPARATUS FOR DRIVING AN ELECTRIC WATCH [75] Inventor: Kinji Fujita, Nagano, Japan [73] Assignee: Kahushiki Kaisha Suwa Seikosha,

Tokyo, Japan [22] Filed: June 30, 1971 [21] Appl. No.: 158,349

[30] Foreign Application Priority Data July 7, 1970 Japan 45/58952 [52] U.S. Cl 58/28 A, 318/130, 331/118 [51] Int. Cl G04c 3/04, H021: 33/16, H03b 5/20 [58] Field of Search 58/23 R, 23 A, 23 AD, 58/28R, 28 A, 28 AD; 318/l30;331/109, 113

[ 5] June 26, 1973 [56] References Cited UNITED STATES PATENTS 3,568,091 3/1971 Rahe 58/113 R 3,363,410 l/l968 Imahashi 58/23 A C X FOREIGN PATENTS OR APPLICATIONS 1,174,332 12/1969 Great Britain 58/28 R Primary Examiner-Stephen J. Tomsky Assistant ExaminerEdith C. Simmons Jackson Att0mey-Alex Friedman, Lawrence Rosenthal et al.

[5 7] ABSTRACT An apparatus for driving an electric watch having a balance wheel which is driven electro-magnetically, wherein driving current is alternately applied in opposite directions to the driving coil.

3 Claims, 13 Drawing Figures PATENIED JUN 26 I875 smears FIG. 4

72; /73 m I?! L FIG. "5(a) BACKGROUND OF THE INVENTION This invention relates generally to the driving arrangement for electro-magnetically driven balance wheels of electric watches. In the art, such driving arrangements have usually incorporated both driving and detecting coils, with a driving current being passed through the driving coil in only one direction. Limitations in space and the necessity for two separate coils has tended to minimize the efficiency which could be achieved by these arrangements. By providing a driving arrangement wherein the current is passed in both directions through the driving coil, a watch having increased efficiency is produced.

SUMMARY OF THE INVENTION Generally speaking, in accordance with the invention, a driving apparatus for an electro-magnetically driven balance wheel is provided, including a driving coil and circuit means for alternately applying a driving current to said driving coil in opposite directions.

The driving circuit is adapted so that said driving current is applied when said balance wheel is substantially at its neutral position. The driving circuit includes complementary switch means connected to function at rest as an astable multivibrator for self starting.

One object of the invention is to use the limited space of an electric coil effectively, to promote the electric driving efficiency of the balance and to reduce the consumption electric power.

Another object of the invention is to improve the starting characteristics of the balance and to provide for the reliable starting of the balance.

A further object of the invention is to symmetrically drive the balance even if the magnetic arrangement produces a non-symmetrical induced voltage, and to stabilize the operation of the balance by reducing escapement errors.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OFTHE DRAWINGS For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1a is a plan view and FIG. 1b a side view of a balance wheel system wherein the balance wheel is provided with permanent magnets;

FIG. 2 shows one embodiment of the conventional type of electric circuit for driving said balance wheel;

FIGS. 3a, 3b and 30 show selected wave forms of electric signals in the driving circuit of FIG. 2;

FIG. 4 shows one enbodiment of the driving circuit according to the invention;

FIGS. 5a, 5b and 5c show waveforms of selected electric signals in the driving circuit according to the invention of FIG. 4 at the starting time of the balance wheel; and

FIGS. 6a, 6b and 60 show waveforms of selected electric signals in the driving circuit according to the invention of FIG. 4 when the balance is oscillating at its normal amplitude.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One enbodiment of a balance wheel system for watches is shown in FIG. 1, wherein l is a balance wheel, 2 a permanent magnet, 3 a plate of magnetic material for completing the magnetic circuit, 4 a balance staff, and 5 an electric coil. The alignment of the permanent magnets and the path of the magnetic field produced thereby are shown in FIG. lb.

FIG. 2 shows one embodiment of a conventional driving circuit utilized with the type of balance of FIG. 1. L1 is a coil which detects the vibration of the balance (hereinafter referred to as a detecting coil). L2 is a coil which drives the balance (hereinafter referred to as a driving coil). T is a transistor for controlling the driving current, C a condenser for blocking the direct current component, and R a bias resistor.

When the balance receives a shock and is vibrated to a certain amplitude, voltage is induced in the detecting coil. As a result of amplification by the transistor, driving electric current is applied to the driving coil, the balance is driven, and the amplitude is increased. The loss energy of the balance and the driving power reach an equilibrium, and the balance is swung constantly.

FIG. 3a shows the detecting voltage waveform, FIG. 3b the driving voltage waveform and FIG. 3c the driving current waveform in the circuit of FIG. 2 at said equilibrium. As is clear from said waveforms, the balance is driven non-symmetrically, so that error in the escapement cannot be eliminated. The driving efficiency of said arrangement is as follows:

"7 (y 7 WW wherein:

y induced voltage V battery voltage i= driving current R coil resistance In order to increase this efficiency, the induced voltage should be increased and the coil resistance should be reduced.

In the driving circuit of FIG. 2, both driving and detecting coils are necessary, and the two coils are wound in a limited space. For this reason it is almost impossible to satisfy both of the above conditions. Thus, in order to obtain the large induced voltage, the turns of the coil should be increased and very thin copper wire should be utilized to conserve space. However, if the copper wire is thin, coil resistance is increased and high efficiency cannot be obtained.

The voltage induced by the magnetic arrangement of the balance as shown in FIG. 1 is non-symmetrical, one part of the induced voltage at each cycle being only about one-half the value of the other portion of the cycle. Driving efficiency is thereby further reduced and low electric consumption cannot be obtained. Further, the utilization of very thin wire increases the cost of raw materials and is not conducive to mass production.

In the driving'circuit shown of FIG. 2, when the amplitude of the balance is smaller than a certain minimum, the transistor will not function as an amplifier, the oscillation of the balance will not increase and the watch may be stopped.

The foregoing defects can be eliminated by the driving arrangement according to the invention, which permits a wide variety of designs of electric watches.

The circuit in FIG. 4 shows one embodiment of the driving arrangement according to the invention. In this circuit, T1, T2, T3, and T4 are switching transistors, R1 and R2 are bias resistors, C a coupling condenser, and L a driving coil.

At starting, i.e., when the amplitude of the balance is zero, the circuit is operated as an astable multivibrator as shown in the waveforms of FIG. 5. FIG. a shows the driving voltage waveform at point p, FIG. Sb shows the driving voltage waveform at point q and FIG. 5c shows the driving current waveform. During the time i, the transistors T1 and T3 are conductive, the transistors T2 and T4 are in the cut off condition, and electric current flows in the driving coil from point q to point p. During the time ii, the respective transistors are in the opposite state and the current in the driving coil is reversed in order to flow from point p to point q.

The values of R1 and C determine the time intervals of times i and ii. Said period may be expressed as:

-r 0.7 RC sec.

The values of R1 and C are selected so that r is set approximately at the oscillating period or longer, so the balance can start even from a completely stationary condition. The voltage induced to the driving coil increases as the amplitude of the balance is increased. This makes the coupling condenser C charge fully, so the conductive pulse width of the transistor is small when the balance oscillates normally as shown in the waveforms of FIG. 6. FIGS. 6a and 6b show the driving voltage waveforms at points p and q respectively, and FIG. 60 shows the driving current waveform.

As understood from FIG. 6, the driving waveform is formed symmetrically, and the balance is driven at the neutral position. This arrangement is favorable where there are errors in the escapement. The driving current flows when the speed of the balance and the induced voltage are the highest, so that driving efficiency is high. The driving arrangement according to the invention does not require a detecting coil. Accordingly, the space for the detecting coil can be used for the driving coil, permitting the forming of the driving coil of thick wire. In this manner, the resistance of the driving coil is reduced while the arrangement is conducive for mass production.

As a result of the development of integrated circuits, the complexity of the circuit according to the invention is not a problem. The circuit may be mass produced in a compact size at high reliability.

By adopting the arrangement according to the invention, low power consumption through high efficiency driving, or high beats of the balance can be obtained.

It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. Apparatus for driving an electric watch comprising displaceable balance means having magnetic means for producing a magnetic field; a driving coil positioned in the path of said magnetic field for displacing said balance means; and circuit means coupled to said driving coil for alternately applying a driving current in opposite directions to said driving coil, said circuit means including complementary switch means having first and second pairs of complementary transistors each having an emitter, collector and base, the emitter to collector path of the transistors defining each of said pairs being in series connection with said driving coil, said first and second pairs of transistors being alternately rendered conductive for the application of driving current to said driving coil so that said circuit means functions as an astable multivibrator at least when said balance wheel is at rest.

2. Apparatus as recited in claim 1, wherein said circuit means includes RC timing means operatively coupled to said complementary switch means for controlling the period of application of driving current to said driving coil in each direction, said RC timing means being selected so that the period of oscillation is equal to or greater than the normal period of oscillation of said balance means.

3. Apparatus as recited in claim 1, wherein said balance means is adapted for oscillation about a neutral position, said circuit means being adapted to apply said driving current to said driving coil when said balance means is substantially at said neutral position. 

1. Apparatus for driving an electric watch comprising displaceable balance means having magnetic means for producing a magnetic field; a driving coil positioned in the path of said magnetic field for displacing said balance means; and circuit means coupled to said driving coil for alternately applying a driving current in opposite directions to said driving coil, said circuit means including complementary switch means having first and second pairs of complementary transistors each having an emitter, collector and base, the emitter to collector path of the transistors defining each of said pairs being in series connection with said driving coil, said first and second pairs of transistors being alternately rendered conductive for the application of driving current to said driving coil so that said circuit means functions as an astable multivibrator at least when said balance wheel is at rest.
 2. Apparatus as recited in claim 1, wherein said circuit means includes RC timing means operatively coupled to said comPlementary switch means for controlling the period of application of driving current to said driving coil in each direction, said RC timing means being selected so that the period of oscillation is equal to or greater than the normal period of oscillation of said balance means.
 3. Apparatus as recited in claim 1, wherein said balance means is adapted for oscillation about a neutral position, said circuit means being adapted to apply said driving current to said driving coil when said balance means is substantially at said neutral position. 